Garmin GNC 420 Maintenance Manual page 70

5.7.2.11 TX Interlock
1. Apply an 10 V, 30% modulated, 1000 Hz RF signal.
2. Measure SNR at rated audio ( 7.07 Vrms).
Sensitivity Reading 1______
3. Enable TX interlock line.
4. Measure SNR again.
Sensitivity Reading 2______
NLT 15dB difference between sensitivity reading 1 and 2
______OK
5. Disable TX interlock line.
5.7.2.12 AGC Test
1. Apply a 30% modulated 1000 Hz RF signal to the unit.
2. Tune the unit to 127.000 MHz. Vary the signal from 5 V to 450mV.
3. Set the volume for rated audio ( 7.07 Vrms).
4. Verify the audio output does not vary by more than 6 dB.
5 V to 450mV ________dB
5.7.2.13 Selectivity (25 kHz Mode)
1. Tune the unit to 127.000 MHz.
2. Turn the modulation OFF on the RF signal generator.
3. Turn the power/volume control knob fully counterclockwise, but not past the detent (OFF)
position.
4. Apply a 10 µV RF signal at 127.000 MHz.
5. Monitor the AGC voltage with the DMM (DC) at J2-2.
6. The DC voltage reading on the DMM is the AGC reference voltage, write it down as you will
need it for the rest of the test.
AGC Reference Voltage ______ VDC
400 SERIES MAINTENANCE MANUAL
P/N 190-00140-05
Page 5-19
Rev. C